Autoscaling_elb
Chapter 7: Auto Scaling & Load Balancing
Section titled “Chapter 7: Auto Scaling & Load Balancing”Building Scalable and Highly Available Applications
Section titled “Building Scalable and Highly Available Applications”7.1 Overview
Section titled “7.1 Overview”Auto Scaling and Elastic Load Balancing work together to provide automatic scaling and high availability for your applications.
Auto Scaling & Load Balancing Architecture+------------------------------------------------------------------+| || Internet || | || v || +---------------+ || | Route 53 | || +---------------+ || | || v || +-----------------------------------+ || | Application Load Balancer | || | (ALB) | || +-----------------------------------+ || | | || v v || +---------------------+ +---------------------+ || | Auto Scaling | | Auto Scaling | || | Group 1 | | Group 2 | || | | | | || | +----+ +----+ +----+| | +----+ +----+ +----+| || | |EC2 | |EC2 | |EC2 || | |EC2 | |EC2 | |EC2 || || | +----+ +----+ +----+| | +----+ +----+ +----+| || | AZ-A AZ-B AZ-C | | AZ-A AZ-B AZ-C | || +---------------------+ +---------------------+ || || Components: || - Load Balancer: Distributes traffic || - Auto Scaling Group: Manages instance count || - Launch Template: Defines instance configuration || |+------------------------------------------------------------------+7.2 Elastic Load Balancing (ELB)
Section titled “7.2 Elastic Load Balancing (ELB)”ELB Types Comparison
Section titled “ELB Types Comparison” Load Balancer Types+------------------------------------------------------------------+| || Application Load Balancer (ALB) || +----------------------------------------------------------+ || | Layer: 7 (HTTP/HTTPS) | || | Features: | || | - Content-based routing | || | - Host-based routing | || | - Path-based routing | || | - WebSocket support | || | - HTTP/2 support | || | - TLS termination | || | Use Cases: | || | - Web applications | || | - Microservices | || | - Containerized applications | || +----------------------------------------------------------+ || || Network Load Balancer (NLB) || +----------------------------------------------------------+ || | Layer: 4 (TCP/UDP) | || | Features: | || | - Ultra-high performance | || | - Static IP address | || | - TLS passthrough | || | - UDP support | || | - Millions of requests/second | || | Use Cases: | || | - Real-time gaming | || | - IoT | || | - Non-HTTP workloads | || +----------------------------------------------------------+ || || Gateway Load Balancer (GWLB) || +----------------------------------------------------------+ || | Layer: 3 (IP) | || | Features: | || | - Transparent network gateway | || | - Third-party security appliances | || | - Inline traffic inspection | || | Use Cases: | || | - Firewalls | || | - IDS/IPS | || | - Deep packet inspection | || +----------------------------------------------------------+ || || Classic Load Balancer (CLB) - Legacy || +----------------------------------------------------------+ || | Layer: 4 & 7 | || | Status: Deprecated (use ALB/NLB instead) | || +----------------------------------------------------------+ || |+------------------------------------------------------------------+ALB Routing Architecture
Section titled “ALB Routing Architecture” ALB Request Routing+------------------------------------------------------------------+| || Client Request || | || v || +---------------+ || | Listener | || | (Port 443) | || +---------------+ || | || v || +---------------+ || | Rules | || | Evaluation | || +---------------+ || | || +------------------+------------------+ || | | | || v v v || +---------+ +---------+ +---------+ || | Rule 1 | | Rule 2 | | Default | || | | | | | Rule | || |Host: | |Path: | | | || |api. | |/images | | | || |example. | | | | | || |com | | | | | || +---------+ +---------+ +---------+ || | | | || v v v || +---------+ +---------+ +---------+ || |Target | |Target | |Target | || |Group 1 | |Group 2 | |Group 3 | || | | | | | | || |API | |Image | |Web | || |Servers | |Servers | |Servers | || +---------+ +---------+ +---------+ || |+------------------------------------------------------------------+Target Groups
Section titled “Target Groups” Target Group Configuration+------------------------------------------------------------------+| || Target Group Settings: || +----------------------------------------------------------+ || | Protocol: HTTP/HTTPS/TCP | || | Port: Application port | || | Health Check: | || | - Path: /health | || | - Interval: 30 seconds | || | - Timeout: 5 seconds | || | - Healthy threshold: 3 | || | - Unhealthy threshold: 2 | || +----------------------------------------------------------+ || || Target Types: || +----------------------------------------------------------+ || | | || | Instance | IP Address | Lambda | || | +----------+ | +----------+ | +----------+ | || | | EC2 | | | Private | | | Function | | || | | Instance | | | IP | | | | | || | | ID | | | Address | | | | | || | +----------+ | +----------+ | +----------+ | || | | | | || | Use: EC2 in ASG | Use: Containers | Use: Serverless | || | | on ECS/EKS | | || +----------------------------------------------------------+ || |+------------------------------------------------------------------+Health Checks
Section titled “Health Checks” Health Check Flow+------------------------------------------------------------------+| || Load Balancer || +----------------------------------------------------------+ || | | || | Health Check Request (every 30s) | || | | | || | v | || | +----------+ +----------+ +----------+ | || | | Target 1 | | Target 2 | | Target 3 | | || | | | | | | | | || | | GET | | GET | | GET | | || | | /health | | /health | | /health | | || | | | | | | | | || | | 200 OK | | 200 OK | | 503 | | || | | HEALTHY | | HEALTHY | | UNHEALTHY| | || | +----------+ +----------+ +----------+ | || | | || | Traffic Routing: | || | - Only routes to HEALTHY targets | || | - Unhealthy targets removed from rotation | || | - Auto Scaling can replace unhealthy instances | || +----------------------------------------------------------+ || |+------------------------------------------------------------------+7.3 Auto Scaling Groups (ASG)
Section titled “7.3 Auto Scaling Groups (ASG)”ASG Architecture
Section titled “ASG Architecture” Auto Scaling Group Components+------------------------------------------------------------------+| || +------------------------+ || | Auto Scaling Group | || +------------------------+ || | || +---------------------+---------------------+ || | | | || v v v || +----------+ +----------+ +----------+ || | Launch | | Scaling | | Health | || | Template | | Policies | | Checks | || +----------+ +----------+ +----------+ || || Launch Template: Instance configuration || Scaling Policies: When to scale || Health Checks: Instance health monitoring || |+------------------------------------------------------------------+Scaling Policies
Section titled “Scaling Policies” Auto Scaling Policies+------------------------------------------------------------------+| || 1. Simple Scaling || +----------------------------------------------------------+ || | | || | CloudWatch Alarm | || | | | || | v | || | +----------+ +----------+ | || | | CPU > 80%| --> | Add 2 | | || | | | | Instances| | || | +----------+ +----------+ | || | | || | Cooldown Period: Wait before next scaling action | || +----------------------------------------------------------+ || || 2. Step Scaling || +----------------------------------------------------------+ || | | || | CPU Utilization Instances to Add | || | +----------------+-------------------+ | || | | 60-70% | +1 instance | | || | | 70-80% | +2 instances | | || | | 80-90% | +3 instances | | || | | > 90% | +4 instances | | || | +----------------+-------------------+ | || +----------------------------------------------------------+ || || 3. Target Tracking || +----------------------------------------------------------+ || | | || | Target: CPU = 50% | || | | || | Actual CPU Action | || | +----------------+-------------------+ | || | | 70% | Scale out | | || | | 40% | Scale in | | || | | 50% | No action | | || | +----------------+-------------------+ | || | | || | AWS automatically adjusts capacity | || +----------------------------------------------------------+ || || 4. Predictive Scaling || +----------------------------------------------------------+ || | | || | Uses ML to predict traffic patterns | || | | || | Time Predicted Traffic Instances | || | +----------------+-------------------+----------------+ | || | | 09:00 | High | 10 | | || | | 12:00 | Peak | 15 | | || | | 18:00 | Low | 5 | | || | +----------------+-------------------+----------------+ | || | | || | Pre-provisions capacity before traffic spikes | || +----------------------------------------------------------+ || |+------------------------------------------------------------------+Scaling Process Flow
Section titled “Scaling Process Flow” Auto Scaling Process+------------------------------------------------------------------+| || Scale Out (Add Instances) || +----------------------------------------------------------+ || | | || | 1. CloudWatch Alarm triggers | || | | | || | v | || | 2. ASG evaluates scaling policy | || | | | || | v | || | 3. Launch new instance using Launch Template | || | | | || | v | || | 4. Instance boots and passes health checks | || | | | || | v | || | 5. Instance added to Load Balancer target group | || | | | || | v | || | 6. Traffic routed to new instance | || | | || +----------------------------------------------------------+ || || Scale In (Remove Instances) || +----------------------------------------------------------+ || | | || | 1. CloudWatch Alarm triggers (low utilization) | || | | | || | v | || | 2. ASG selects instance to terminate | || | | | || | v | || | 3. Instance enters Standby or Terminate | || | | | || | v | || | 4. Connection draining (if enabled) | || | | | || | v | || | 5. Instance removed from target group | || | | | || | v | || | 6. Instance terminated | || | | || +----------------------------------------------------------+ || |+------------------------------------------------------------------+Instance Protection
Section titled “Instance Protection” Instance Protection Options+------------------------------------------------------------------+| || Scale-In Protection || +----------------------------------------------------------+ || | | || | Protected Instances (not terminated during scale-in) | || | | || | +----------+ +----------+ +----------+ | || | | Instance | | Instance | | Instance | | || | | 1 | | 2 | | 3 | | || | | [LOCK] | | | | [LOCK] | | || | |Protected | | Can be | |Protected | | || | +----------+ |terminated| +----------+ | || | +----------+ | || | | || | Enable: | || | aws autoscaling set-instance-protection \ | || | --instance-ids i-12345 \ | || | --protected-from-scale-in | || +----------------------------------------------------------+ || || Standby State || +----------------------------------------------------------+ || | | || | Instance in Standby: | || | - Not serving traffic | || | - Not replaced by ASG | || | - Can be updated/troubleshooted | || | | || | Enter Standby: | || | aws autoscaling enter-standby \ | || | --instance-ids i-12345 \ | || | --auto-scaling-group-name my-asg | || +----------------------------------------------------------+ || |+------------------------------------------------------------------+7.4 Load Balancer Integration
Section titled “7.4 Load Balancer Integration”ALB + ASG Architecture
Section titled “ALB + ASG Architecture” Complete ALB + ASG Setup+------------------------------------------------------------------+| || Internet || | || v || +---------------+ || | Route 53 | || | (DNS) | || +---------------+ || | || v || +-----------------------------------+ || | Application Load Balancer | || | | || | Listeners: | || | - Port 80 (HTTP) -> Redirect | || | - Port 443 (HTTPS) | || | | || | Target Groups: | || | - Web-TG (Port 8080) | || | - API-TG (Port 3000) | || +-----------------------------------+ || / \ || / \ || v v || +---------------------+ +---------------------+ || | Auto Scaling | | Auto Scaling | || | Group: Web | | Group: API | || | | | | || | Min: 2 | | Min: 2 | || | Max: 10 | | Max: 20 | || | Desired: 3 | | Desired: 5 | || | | | | || | +----+ +----+ +----+| | +----+ +----+ +----+ +----+ +----+| || | |Web | |Web | |Web || | |API | |API | |API | |API | |API || || | +----+ +----+ +----+| | +----+ +----+ +----+ +----+ +----+| || +---------------------+ +---------------------+ || |+------------------------------------------------------------------+7.5 Practical Configuration
Section titled “7.5 Practical Configuration”Terraform: ALB + ASG
Section titled “Terraform: ALB + ASG”# ============================================================# Application Load Balancer# ============================================================
resource "aws_lb" "main" { name = "my-alb" internal = false load_balancer_type = "application" security_groups = [aws_security_group.alb.id] subnets = var.public_subnet_ids
enable_deletion_protection = false}
resource "aws_lb_target_group" "web" { name = "web-tg" port = 8080 protocol = "HTTP" vpc_id = var.vpc_id
health_check { enabled = true healthy_threshold = 3 interval = 30 matcher = "200" path = "/health" port = "traffic-port" protocol = "HTTP" timeout = 5 unhealthy_threshold = 2 }}
resource "aws_lb_listener" "https" { load_balancer_arn = aws_lb.main.arn port = "443" protocol = "HTTPS" ssl_policy = "ELBSecurityPolicy-2021-06" certificate_arn = var.certificate_arn
default_action { type = "forward" target_group_arn = aws_lb_target_group.web.arn }}
# ============================================================# Auto Scaling Group# ============================================================
resource "aws_launch_template" "web" { name_prefix = "web-" image_id = var.ami_id instance_type = "t3.medium" key_name = var.key_name
iam_instance_profile { name = aws_iam_instance_profile.web.name }
network_interfaces { associate_public_ip_address = false security_groups = [aws_security_group.web.id] }
user_data = base64encode(<<-EOF #!/bin/bash yum install -y httpd systemctl start httpd EOF )
tag_specifications { resource_type = "instance" tags = { Name = "WebServer" } }}
resource "aws_autoscaling_group" "web" { name = "web-asg" vpc_zone_identifier = var.private_subnet_ids
min_size = 2 max_size = 10 desired_capacity = 3
launch_template { id = aws_launch_template.web.id version = "$Latest" }
target_group_arns = [aws_lb_target_group.web.arn]
health_check_type = "ELB" health_check_grace_period = 300
tag { key = "Name" value = "WebServer" propagate_at_launch = true }}
resource "aws_autoscaling_policy" "scale_out" { name = "scale-out" scaling_adjustment = 2 adjustment_type = "ChangeInCapacity" cooldown = 300 autoscaling_group_name = aws_autoscaling_group.web.name}
resource "aws_cloudwatch_metric_alarm" "high_cpu" { alarm_name = "high-cpu" comparison_operator = "GreaterThanThreshold" evaluation_periods = "2" metric_name = "CPUUtilization" namespace = "AWS/EC2" period = "120" statistic = "Average" threshold = "80"
dimensions = { AutoScalingGroupName = aws_autoscaling_group.web.name }
alarm_actions = [aws_autoscaling_policy.scale_out.arn]}7.6 Best Practices
Section titled “7.6 Best Practices” Auto Scaling & Load Balancing Best Practices+------------------------------------------------------------------+| || 1. Multi-AZ Deployment || +----------------------------------------------------------+ || | - Deploy across minimum 2 AZs | || | - Use all available AZs for maximum availability | || | - Configure subnets in each AZ | || +----------------------------------------------------------+ || || 2. Health Check Configuration || +----------------------------------------------------------+ || | - Use meaningful health check endpoints | || | - Set appropriate thresholds | || | - Configure grace period for instance startup | || +----------------------------------------------------------+ || || 3. Scaling Policies || +----------------------------------------------------------+ || | - Use target tracking for simplicity | || | - Set appropriate cooldown periods | || | - Consider predictive scaling for known patterns | || +----------------------------------------------------------+ || || 4. Instance Warm-up || +----------------------------------------------------------+ || | - Allow time for instance initialization | || | - Use lifecycle hooks for custom initialization | || | - Configure appropriate grace period | || +----------------------------------------------------------+ || || 5. Monitoring || +----------------------------------------------------------+ || | - Monitor scaling activities | || | - Set up CloudWatch alarms | || | - Use ASG notifications | || +----------------------------------------------------------+ || |+------------------------------------------------------------------+7.7 Exam Tips
Section titled “7.7 Exam Tips”
- ALB vs NLB: ALB for HTTP/HTTPS (Layer 7), NLB for TCP/UDP (Layer 4)
- Target Groups: Can target instances, IPs, or Lambda functions
- Health Checks: ELB health checks + EC2 health checks for ASG
- Scaling Policies: Target tracking is simplest, step scaling for granular control
- Cooldown: Prevents rapid scaling cycles
- Instance Protection: Prevents scale-in termination
- Connection Draining: Allows in-flight requests to complete
- Cross-Zone Load Balancing: Distributes traffic evenly across AZs
Next Chapter
Section titled “Next Chapter”Chapter 8: AWS Lambda - Serverless Computing
Last Updated: February 2026